Pet artificial aggregate for the preparation of lightened concrete

ABSTRACT

Lightweight artificial aggregate in sanded or non-sanded PET for the production of light or lightened structural and nonstructural concrete or materials for building industry, and a process for the preparation thereof.

The present invention provides a novel lightweight PET(polyethylenterephtalate) artificial aggregate for the production oflightened structural and non-structural concrete or materials forbuilding industry, and a process for the preparation thereof.

BACKGROUND OF THE INVENTION

According to the UNI normative, light or lightened concrete has anapparent volume mass of from 200 to 2000 Kg/m³, that is, lower than thatof conventional concrete (around 2400 Kg/m³). Important advantages areassociated with the use of light concrete, for example, reduced weightand size of building structures, reduced foundation-ground load, reducedseismic actions. Light or lightened concrete is prepared by replacingcommon aggregates with light aggregates, such as expanded clay,pearlite, vermiculite, rottenstone, lapilli, polystyrene. However, onlyfew light aggregates are suitable for the production of structuralconcretes, i.e. concrete with compression cubic resistance higher than15 N/mm².

DESCRIPTION OF THE INVENTION

It has now been found that a lightweight artificial aggregate consistingof PET granules provides structural and non structural concrete withproperties of lightness, workability, mechanical resistance, durabilityand low thermal conductivity.

The lightweight artificial aggregate according to the invention iscomposed of PET granules, which can be coated with fine or coarse sandto improve the adherence between grains and mortar.

In the preparation of the aggregate, PET material from differentsources, including recycled PET bottles, is reduced into flakes whichare then subjected to a thermal and mechanical process thus forming aresistant, light aggregate. This aggregate, which will be referred to as“non-sanded” lightweight PET aggregate, can be used as such in thepreparation of non-structural concrete. In alternative, the surface ofthe PET aggregate is covered or coated with sand, thus forming a“sanded” aggregate suitable for the manufacture of structural concrete.

In a preferred embodiment of the invention, sanded and non-sanded PETaggregates are produced as follows. A defined amount of PETflakes—depending on the desired granulometry and the volume mass of thegranule—is placed in a ventilated oven and heated to a temperature of250-260° C. for a time sufficient for flakes to curl and for theirsurface to soften, at the same time applying a vibratory and rotationalmechanical movement to increase the number of contacts between flakes.When heating is ended, the aggregated flakes are subjected to acontrolled pressure that gives them a spheroid shape. The appliedcompression strength determines the final resistance of the grain. It isimportant that during the process, PET does not reach complete melting.The thus produced non-sanded PET aggregate can be further processed toobtain a sanded aggregate. In this case, PET granules are subjected tosurface flaming and rolled on fine or coarse sand to obtain uniformcoating of the granules.

Sanded and non-sanded aggregates are separated by size with anappropriate sieve. The aggregates can have different sizes, ranging from1 to 40 mm, which correspond to different resistance classes. Dependingon the compression strength applied during granule formation, the numberand size of the empty spaces within grains change and the mechanicalresistance changes accordingly.

The aggregates are classified as i) fine, when the size does not exceed3 mm, ii) medium, between 3 and 7 mm, and iii) coarse, over 7 mm.

The heap weight of the PET aggregate depends on the granulometry andcompression strength, but it is generally comprised between 100 and 1100Kg/m³. By way of example, an aggregate in sanded PET with coarse sizebetween 17 and 20 mm and subjected to low compression degree, has a heapweight of approximately 520 Kg/m³.

The lightweight artificial aggregate of the invention allows to prepareconcrete with good mechanical resistance and a lower weight/volume ratio(<2000 Kg/m³) than conventional concrete. The concrete produced from PETaggregates possesses insulating properties due to the low thermalconductivity of PET. Examples of concrete/materials for buildingindustry that can be produced from lightweight sanded-PET artificialaggregates include, but are not limited to, lightened structuralconcrete and concrete of the SCC type (Self-Compacting Concrete).Non-sanded aggregates are preferably used in the preparation ofnon-structural concrete as well as loose material for fillings withthermal and acoustic insulation properties, especially for aggregateswith big grain size.

Since the aggregates can be produced from recycled materials, especiallyfrom recycled plastics such as PET bottles, their use in the preparationof concrete according to the present invention may provide an importantcontribution to waste disposal thus reducing the environmental impact ofplastic wastes.

DESCRIPTION OF THE FIGURES

FIG. 1: granule of the artificial aggregate in “sanded PET”

FIG. 2: Coarse-size aggregate

FIG. 3: PET “flakes” used in the production of the artificial aggregate

FIG. 4: Curled flakes

FIG. 5: PET granules after forming

TABLES

Lightweight Structural Concrete TABLE 1 Properties of sanded lightweightPET aggregate Diameter (mm) 13-20 Heap weight (Kg/m³) 520 Grain weight(Kg/m³) 1316 Surface sanded Water absorption negligible

The used formula is reported in table 2 showing that the mostunfavourable condition has been chosen: a small quantity of concrete, ahigh ratio water/cement, a PET volume percentage equal to the 60% of theentire aggregate. TABLE 2 Mix Design of the structural concretelightened with light artificial aggregate in “sanded” PET CEM I 42.5 R285 Kg/m³ Aggregate PET (13-20 mm) 557 Kg/m³ Crusher sand 761 Kg/m³Water 170 l/m³ Super-plasticizer 2.9 l/m³ Ratio water/cement 0.6Consistence S5 Volume mass 1780 Kg/m³ Compression resistance (28 dd) 27Mpa

Lightweight Aggregate of Big Grain Size for Fillings TABLE 3 Propertiesof lightweight PET aggregate. Diameter (mm) 15-25 Heap weight (Kg/m³)400 Surface not sanded Water absorption NegligibleThe material is resistant, light, non conductive, invariable in time; itresists distorsion also at high temperatures (not far from fusion point)and does not go rotten. If burned, it does not emit toxic gases.

1. An aggregate of PET (polyethylenterephtalate) granules for themanufacture of lightened concrete.
 2. An aggregate according to claim 1,wherein the granules are in the form of flake aggregates.
 3. Anaggregate according to claim 2, wherein the flakes are produced fromrecycled PET bottles.
 4. An aggregate according to claim 1, which iscoated with sand.
 5. A process for the preparation of the aggregateaccording to claim 1, which comprises the following steps: a) reducingPET material into flakes; b) subjecting the PET flakes to a thermal andmechanical process to form flake aggregates;
 6. A process for thepreparation of the aggregate according to claim 4, which comprises thefollowing steps: a) reducing PET material into flakes; b) subjecting thePET flakes to a thermal and mechanical process to form flake aggregates;c) coating PET flake aggregates with sand.
 7. A process according toclaim 6, which comprises: a) providing PET flakes; b) placing the flakesin a ventilated oven and heating to a temperature of 250° C.-260° C.,applying a vibratory and rotational mechanical movement, to obtain flakeaggregates; c) compressing flake aggregates from step (b), to obtain PETgranules;
 8. A process according to claim 7, which comprises a)providing PET flakes; b) placing the flakes in a ventilated oven andheating to a temperature of 250° C.-260° C., applying a vibratory androtational mechanical movement, to obtain flake aggregates; c)compressing flake aggregates from step (b), to obtain PET granules; d)subjecting PET granules to surface flaming and rolling the same on sandto obtain aggregates of coated PET granules;
 9. PET aggregate obtainableby the process of claim
 7. 10. The use of a PET aggregate for thepreparation of structural or non-structural concrete or materials forbuilding industry.
 11. The use according to claim 10 of a PET aggregatecoated with sand.
 12. Lightened concrete or materials for buildingindustry containing a PET aggregate of claim
 1. 13. A concrete ormaterial for building industry according to claim 13, which isstructural and non-structural concrete, self-compacting concrete andthermally and acoustically insulated filling material.